Animal experts said they were surprised by the animals’ consistency during the attacks.

"The number of bites per victim is a little bit astounding to me," George Parsons, director of fishes at Shedd Aquarium in Chicago, said on MPR's All Things Considered on Friday. "Usually they'll bite three or four times and then kind of give up."

Though otter attacks are uncommon, Parsons pointed out that sometimes the animals will use their very sharp teeth to protect their young if they feel threatened. He also said that otter habitats are being threatened by development, which increases the chance that they will come into contact with humans.

If swimmers see otters, they should “be as loud and boisterous as possible” to chase them away, Parsons told MPR. They should also stay clear of areas where they see otters with young pups.